Recently, quantum structures such as quantum dots and quantum wires (referred to as “nanostructure” hereinafter) have vigorously been studied for the purpose of exhibiting new functions or upgrading the existing capabilities in a device that cannot be in a bulk form. One of the known structures used for forming these nanostructures is called “step-and-terrace structure formed on the surface of the single crystalline substrates. The terraces of the step-and-terrace structure configure flat faces at the level of an atomic layer, whereas the steps each configure a height difference equal to the size of a unit cell of a substrate material, or integer multiple or half-integer multiple of the unit cell size. The step-and-terrace structure, therefore, is used for the purpose of forming such nanostructure that repeats regularly or cyclically. There has been studied a method for using, for example, a sputtering method, a laser ablation method, and an MBE method to regularly or cyclically dispose a plurality of materials, starting from the boundary (step edge) between the step and the terrace, in order to create a one-dimensional quantum wire (nanowire).
As a method for creating the step-and-terrace structure onto an oxide crystal, there is known a method of combining an annealing step performed in the atmosphere at approximately 1000° C. and a wet etching step using acid. For instance, it has been reported that a step-and-terrace structure that has a TiO2 terminated terrace face can be obtained by etching a surface of a strontium titanate (SrTiO3) (100) plane oriented single-crystal substrate with BHF (buffered hydrofluoric acid) (Non-patent Document 1).
Patent Document 1 (Japanese Patent Application Publication No. 2000-159600) discloses producing a step-and-terrace structure on a strontium titanate substrate by cutting its surface in a face orientation inclined from a (100)-plane, so that the formed steps extend in the direction of a [001] axis (paragraph [0018] in Patent Document 1). Patent Document 1 also discloses that the levels of the steps of the step-and-terrace structure change depending on the time required for a thermal treatment (paragraphs [0019] and [0020] in Patent Document 1).    Patent Document 1: Japanese Patent Application Publication No. 2000-159600 (e.g., paragraphs [0018] to [0020])    Non-patent Document 1: M. Kawasaki et al., “Atomic control of the SrTiO3 crystal surface,” Science vol. 266, pp. 1540-1542 (1994)